The invention concerns a cable pulley block and, in particular, a technique for detachable fastening of a cable to a cable drum, especially a wire cable.
Cable fastenings to winding drums or cable drums of a hoisting mechanism are machine elements with very high quality demands for safety considerations; their design is regulated in various standards, such as DIN 15020 and EN 14492-2. At the lowest position of a carrying device, there must still be at least two cable turns on the winding drum, and the cable end fastening on the winding drum must be constructed so that, allowing for the friction of the turns remaining on the winding drum, 2.5 times the cable traction force can be sustained, given a coefficient of friction of μ=0.1 between wire cable and base. Guidelines and dimensions for the fastening are set forth, for example, in the Stahl-Eisen-Betriebsblatt (SEB) 666211. The cable ends here are usually incandescently cut or wound with wire.
It is known to provide the cable end with a press-on thickening, usually cylindrical end sleeves of various materials, which, at the same time, make it easy to introduce the end into a continuous opening essentially passing transverse through the wall of the drum into the inside of the winding drum, where the cable end with its thickening is accommodated in a recess cast into the cable drum, made from a casting material, and removably secured as needed. Such a solution is specified, for example, in German Patent DE 101 07 390 C1.
The press-on thickenings of cable ends, also known as press sleeves, can withstand greater cable tractive forces on the drum than the most often used cable clamps with screw fastening per SEB 666211 for the same space required. Because fewer fastening turns are required than with screw clamps, the press sleeves allow for generally shorter drum lengths for the same usable cable length, which besides saving costs also allows a more favorable utilization of space. Moreover, the installation cost when using press sleeves to mount the end of the cable on the cable drum is considerably reduced compared to the solution with a screw clamp. Another benefit of the press sleeve is the fact that one can recognize a proper form-fitted installation from afar and the risk of improperly tightened screws, not permanently secured because wrongly set, is ruled out.
The cable end fastening familiar from German Patent DE 101 07 390 C1 proposes casting specially shaped pockets in the periphery of the drum tube, which accommodate the press sleeves. However, this assumes that the drum tube is made as a cast piece, which is not always the case today. Quite often, not least for cost reasons, cable drums are made from seamless rolled tubes or round rolled plates with a longitudinal welded seam. On such cable drums, a fastening of press sleeves in the manner described above is not possible.
The same holds for a solution as described by U.S. Pat. No. 2,329,943 and which, likewise, uses a cast cable drum. In the case of the cable end fastening specified therein, the press sleeve placed on the cable end after being inserted through the continuous opening is held by a connection piece, which is screwed into a cast-on recess of the cable drum in the region of the intended continuous opening for the end of the cable. The connection piece closes the continuous opening enough to block and retain the thickening of the cable end on the inside of the winding drum. The connection piece and winding drum are intricately manufactured shaped parts adapted to each other, and while it is possible to loosen the fastening of the cable end from the drum with them, their manufacture and use is costly and time-consuming.
DE 625 612 discloses a device for fastening a cable end to a cable drum, in which a roughly C-shaped cable hook is inserted into a keyhole-shaped slot in the cable drum and secured in the slot by a 180° twist. The cable is inserted into the cable hook by means of a grommet thimble.
DE 687 945 discloses the fastening of a cable in a holder screwed to the cable drum by means of an enlarged cable end.